The proposed multisite research project seeks to advance our understanding of the neural mechanisms underlying human spatial memory. Epileptic patients undergoing surgical/invasive monitoring as part of the clinical treatment of drug-resistant epilepsy will be recruited at four major medical centers. This procedure is performed with the highest standard of care and is potentially curative for the patients. By performing game-like spatial memory tasks while undergoing invasive electrode monitoring, patients may provide exquisite data on the brain mechanisms underlying spatial cognition. The proposed studies will examine the relation between brain waves (oscillations), cellular responses, and subjects'behavior during several variants of Yellow Cab, a virtual taxi-driver game. Our first two aims focus on the coding of spatial information. Aim 1 seeks to answer the question: How is the information necessary for (virtual) spatial navigation and spatial memory represented by neuronal activity in various brain regions? Aim 2 attempts to complement this knowledge by asking the question: How do these spatially-relevant neural systems code information? The third, fourth, and fifth aims regard the spatial memory system as a dynamic entity, and investigate the ways in which the responses of this system change over time, due to learning and to modifications of the environment. Aim 3 addresses the question of how spatial representations are acquired and transformed through experience. Aim 4 examines the contextual dependence of human spatial representations, both at the level of environments and at the level of routes within an environment. Finally, Aim 5 investigates the interaction between spatial memory and verbal episodic memory. The research supporting this aim will enable us to link our research on spatial memory to the larger literature on the role of the MTL system in declarative memory processes in humans and animals (Cohen &Eichenbaum, 1993). The proposed studies are of direct relevance to the treatment of epilepsy, in which mapping of cognitive functions to brain regions during surgical procedures is crucial for ensuring good postsurgical outcome.